Radiation therapy has been employed to treat tumorous tissue. In radiation therapy, a high energy beam is applied from an external source towards the patient. The external source, which may be rotating (as in the case for arc therapy), produces a collimated beam of radiation that is directed into the patient to the target site. The dose and placement of the dose must be accurately controlled to ensure that the tumor receives sufficient radiation, and that damage to the surrounding healthy tissue is minimized.
Sometimes, in a radiation treatment procedure, a plurality of treatment sessions may be performed. In each treatment session, a radiation source may be placed at a prescribed gantry angle to thereby deliver radiation beam towards a target tissue from a certain angle. As a result of delivering radiation towards the target tissue from a plurality of different angles, a sufficient radiation dose may be delivered to the target tissue to thereby treat the target tissue, while surrounding healthy tissue may be protected.
It has been known that delivering radiation towards a target tissue from different angles may result in creation of hotspot(s) at critical organ(s) that contains healthy tissue. Currently, hotspots are attempted to be minimized or reduced by drawing or inputting artificial structures representing normal (healthy) tissues into a computer program. Thereafter, the computer program imposes a constraint (representing a limit on radiation dose to be received by the critical organ) on the drawn artificial structures, and determines a treatment plan based on the imposed constraint. In existing techniques, different critical organs with different biological characteristics are considered the same way during treatment planning and treatment execution. For examples, radiation doses (simulated or actual) delivered to different critical organs are accumulated using the same technique. Also, in existing techniques, the same type of dose constraint may be imposed for different critical organs. Inventor of the subject case determines that such existing techniques may not provide a desired treatment plan or a desired treatment result since different critical organs have different biological characteristics, and therefore, should be considered differently during treatment planning and execution.